1. Field of the Invention
The present invention relates to a plasma processing system and method, particularly, a plasma processing system and method appropriately suitable to applications such as etching and film formation on a surface of an object to be processed by irradiating a neutral particle beam, which comprises only electrically neutral particles (atoms and molecules), onto the surface of the object to be processed.
2. Description of the Prior Art
One processing system which uses plasma is a dry etching system. This dry etching system has generally employed an etching method according to which a reactive gas is plasmatized by high frequency glow discharge (RF discharge) to produce ions and chemically active neutral species. These ions and neutral chemical species are transported to a surface of an object to be processed and reacted thereon, thereby the etching is carried out.
In the above described etching method, an object to be processed having a surface covered with an etching mask is set on a high frequency electrode. An action in an incident direction is accelerated by accelerating the positive ion in a direction vertical to the surface of the object with a negative bias potential induced on the surface of the object, thereby it is intended to attain high precision processing with high anisotropy faithful to the above etching mask.
In the above etching method, however, an isotropic etching with an undirectional radical (neutral chemical species) is simultaneously carried out since the above radical is electrically neutral. Therefore, a side etching also proceeds and it is difficult to attain a complete anisotropic form; for example, this side etching is a large problem in a fine work on semiconductors in terms of submicron.
To solve this side etching problem, there have been proposed a method for forming a protective film which prevents reactions on a side wall of a part to be processed (etched part), and a method for controlling a radical reaction on the side wall by lowering the temperature of an object to be processed or an etching method by producing a plasma with a higher ion density, a low pressure and a low radical density.
These methods use positive charged ions which are aligned in the direction. Therefore, since the direction of movement of the ions depends on the associated electric field, the following problems are expected in a fine pattern etching in terms of submicron.
FIG. 14 shows a part near the surface of an object 10 being etched and the surface of the object 10 to be processed is covered with the etching mask 12.
When the etching is proceeded as shown in FIG. 14, the incident direction of ion I is bent due to a disturbance (unevenness) of electric field E (shown with broken lines) along the surface of the object 10 to be processed and the ion I strikes against the side wall to cause side etching. Therefore, an expected anisotropy cannot be obtained and the etching accuracy deteriorates.
Further, at the etching parts 14, 16 and 18, the ion flux which reaches the bottom, for example, 14A, reduces and therefore the so-called micro loading effet (or RIE lag) is caused in which the etching speed on the etching parts (16 and 18 in the drawing) with fine patterns is slower than that on the etching part 14 with a wide pattern.
Furthermore, the ion has a large secondary electron emission coefficient and therefore, when the ion I strikes against the object 10 to be processed, the secondary electron emission takes place on the surface of the object 10 and the etching accuracy deteriorates.
In addition, when the ion is incident onto the surface of the object to be processed, a charge-up occurs on the insulation film since the ion has an electric charge, and a dielectric breakdown may be caused due to the charge-up to deteriorate the film quality and therefore there remains also a problem of reliability deterioration.
Accordingly, it is preferable for ensuring a favorable anisotropy, control of the micro loading effect and improvement of the reliability to carry out the etching with a neutral particle beam composed of active species which are electrically neutral with aligned directions and small secondary electron coefficients.
As a method for implementing a neutral particle beam which meets the above described object have been known a method disclosed in the Japanese Patent Laid Open No. Sho. 62-37382 and Sho. 62-174917 which, for example, uses electron attachment for obtaining a neutral particle beam by neutralizing the ion beam through the electron supply source (neutralizer) such as a filament and a method disclosed in the Japanese Patent Laid Open No. Sho. 61-248428, Sho. 62-174917 and Sho. 62-259443 which use a charge exchange reaction for obtaining a neutral particle beam composed of the radical and others by charge exchange of the same type of ion and radical.
However, the above method utilizing electron attachment cannot provide a sufficient beam flux since the probability of electron attachment is low and it is difficult to efficiently neutralize the ion beam. Therefore a method capable of eliminating such demerit uses a saddle field type ion source to allow improvement of the neutralizing efficiency to 90% or over by appropriately setting the conditions. (Vacuum, 38(6), 469 (1988), etc.)
In the case of the method using the above described charge exchange reaction, the neutralizing efficiency is low since the possibility of charge exchange reaction by incident ions is only once per ion. Therefore the Japanese Patent Laid Open No. Sho. 63-318058 discloses an art capable of raising the neutralizing efficiency by using an element such as Ne (neon) which is light but has a large cross section for charge exchange (ion neutralizing probability).
However, those methods for obtaining a high speed neutral particle beam by the above described charge exchange of ions and for obtaining a neutral particle beam by neutralization with electrons cannot produce a neutral particle beam with aligned directions (high directionality) in a wide area and therefore these methods accompany a problem that high accuracy processing such as etching cannot be achieved on an object with a large area.
In case of the method for obtaining a neutral particle beam by charge exchange of ions as described above, there is a problem that the collision frequency of ions in the charge exchange chamber is low since the charge exchange chamber where electric charges of ions are exchanged and the processing chamber where the object is processed with a neutral particle beam are kept in a substantially same low pressure condition of, for example, 10.sup.-3 Torr and therefore a sufficient charge exchange efficiency (the number of neutral particles produced to the number of ions introduced) cannot be obtained and the processing speed for the object to be processed is also low.
Further, a necessity for improving the charge exchange efficiency to increase the processing speed on an object to be processed encounters with a problem that the apparatus will be inevitably large in size because a sufficient ion flying distance should be ensured.
The method using the above described saddle field type ion source has a problem that the energy and flux of the neutral particle beam produced cannot be independently controlled, the energy of the beam obtained is relatively high (approximately 1 k eV or over) and the width of energy distribution is large.
The art disclosed in the above Japanese Patent Laid Open No. Sho. 63-318058 is disadvantageous in that the etching speed in the etching with a light element such as Ne is several times less than that in case of the etching with a heavier element such as Ar or Kr since the etching yield in the former case is small and consequently an increase of neutralizing efficiency is offset and the types of usable elements are limited.
The current art utilizing charge exchange reaction has a problem that the etching speed is low since the flux of neutral particle beam produced is small. If it is attempted to raise the etching speed to a practically available level to solve this problem, the energy of neutral particles is required to be approximately several hundreds of eV and an opposite effect against the general tendency to less energy. Accordingly, an important point to raise the etching speed to a practical level by a neutral particle beam generating method which utilizes charge exchange reaction is how to generate a low energy neutral particle beam as much as possible and increase the neutral particle beam flux.
The method utilizing the above charge exchange reaction is disadvantageous in that neutral particles as described above are less reactive when they are entered into the object to be processed and therefore a sufficient etching speed (depositing speed in case of film formation) cannot be obtained since neutral particles are only given translation energy.